This invention relates to a water-swellable thermoplastic bonding and coating composition based on a water-insoluble component, a water-soluble or water-dispersible component and a water-swellable component. The invention also relates to the use of this thermoplastic composition for the production of watertight constructions, more particularly for the production of longitudinally watertight cable constructions.
A number of constructions, for example pipelines and, in particular, underground or underwater cables, have to be protected against penetrating water at junctions and joints or in the event of damage to their outer casings. Power and/or telecommunications cables in particular are long-life capital goods whose reliability has to be guaranteed over a very long period. In the event of damage to the outer insulation and/or at faulty junctions, water penetrates into such cable constructions and can cause serious damage to the cable. Water can spread rapidly along the cable so that a cable damaged in this way can be become unusable over long stretches.
To prevent water from penetrating into such constructions, it has been common practice for some time to use water-swellable sealing materials or sealing constructions. JP-A-58-215334 (83) describes in general terms heat-curing sealing materials based on rubbers and a water-swellable polyurethane resin based on ethylene oxide/propylene oxide copolymers.
According to the prior art, multilayer sealing systems are used for the production of longitudinally watertight power and telecommunications cables. Thus, in xe2x80x9cDraht und Kabelpanoramaxe2x80x9d, May/June/July 1988, W. Schxc3xa4fer and P. Graber describe swellable xe2x80x9cnonwovensxe2x80x9d of an extremely homogeneous swelling layer, consisting of a mixture of a synthetic hydrogel former (swelling powder) with chemically pure cellulose pulp as filler, and a high-strength carrier layer of polyester fibers with polyester filaments as an additional reinforcing element. These two layers are thermally united solely by applying heat and high pressure, i.e. without using low-melting thermoplastics. Swellable bandages are then made from these nonwovens or yarns and wrapped around the bundle of wires, optionally together with an inner plastic sheath.
EP-A-188 959 describes a multilayer sealing tape consisting of a support of paper, textiles or plastics which are coated with a layer of a water-swellable polymeric powder and a water-soluble binder and optionally a surfactant.
U.S. Pat. No. 5,020,875 describes cable constructions in which the layer intended to keep water out by swelling consists of a multilayer laminate. This laminate consists of two support tapes of a hydrophobic material, for example polyester. A water-swellable polymer or copolymer of the superabsorber type is arranged between these two support tapes.
U.S. Pat. No. 5,188,883 describes a multilayer composite structure of a metal tape as one layer and a layer of a swellable water-blocking material, these two layers and surfaces being joined by an adhesive.
The invention is a water-swellable thermoplastic bonding and coating composition comprising a water-insoluble component A, wherein component A comprises at least one water-insoluble (co)polymer and at least one other resin, a water-soluble or water-dispersible component B, wherein component B comprises at least one water-soluble or water-dispersible oligomer and/or (co)polymer, and a water-swellable component C, wherein component C comprises a water-swellable (co)polymer, wherein components A, B and C are homogeneously mixed and its use in watertight constructions, more particularly for the production of longitudinally watertight cable constructions.